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<br />1'- <br />r"- <br />CD <br />W <br />o <br /> <br />The relatively low infiltration rates and slow capillary movement of <br /> <br />~ <br />'-' <br /> <br />water necessitate long irrigation time periods to attain reasonable amounts <br /> <br />of infiltration, especially in the spring when the soil is dry. The average <br /> <br />irrigation application time is 27.7 hours and varies from 24 to 48 hours. It <br /> <br />typically takes an average of 6.6 hours for the flow in the furrow to advance <br /> <br />to the end of a field (average length of 970 feet). <br /> <br />Farm Ditch Seepage <br /> <br />The farm ditches contribute an estimated 1,090 acre-feet per year to the <br /> <br />ground-water system in the Reed Wash study area, based on the following <br /> <br />assumptions: <br /> <br />1. 38 miles of unlined head ditches which convey water for 100 <br /> <br />days per year. <br /> <br />2. 58 miles of unlined tailwater ditches which are full 30 days <br /> <br />per year. <br /> <br />3. The ditch seepage was calculated to be one-third the rate of <br /> <br />the lateral seepage (estimated average wetted perimeter (W.P.) <br /> <br />of ditches 2.5 feet ~ average wetted perimeter of laterals of <br /> <br />7.4 feet is approximately 1/3), or 0.10 ds per mile, using <br /> <br />approximations of average wetted perimeters. Usin!: a typical <br /> <br />hydraulic conductivity CK) of 0.7 inch per hour for soils in the <br /> <br />area yields loss rates (q) of 0.06 cfs per mile with the formula <br /> <br />q=KCW.P.). <br />3.5 <br /> <br />Ditch seepage was estimated at 26 percent of the lateral seepage in the <br /> <br />Reed Wash study area. <br /> <br />16 <br />